My wife stood before me with some items in front of her. Without a word, she emptied a large jar of mayonnaise and proceeded to fill the empty jar with rocks right to the top, rocks about 2" diameter, then asked me if the jar was full. I agreed that it was.
She then picked up a box of pebbles and poured them in to the jar. She shook the jar lightly. The pebbles, of course, rolled into the open areas between the rocks. My wife then asked me if the jar was now full. I agreed that, yes, it was.
She then poured a bag of sand into the jar with the result that the sand filled up the remaining spaces between the rocks and pebbles.
"Now," said my wife, "I want you to recognize that this is your life. The rocks are the important things - your family, your wife who loves you, your health, your children - anything that is so important to you that if it were lost, you would be nearly destroyed. The pebbles are the other things in life that matter, but on a smaller scale. The pebbles represent things like your job, your house and your car. The sand is everything else. The small stuff. Your X-box, football, the pub, porn. If you put the sand or the pebbles first, there is no room for the rocks. The same goes for your life.
If you spend all your energy and time on the small stuff, material things, you will never have room for the things that are truly most important."
I was dumbfounded. So where was she going to get more mayonnaise from for my sandwich?